The invention is concerned with herbicidal(bisalkoxycarbonyl)-alkyl 5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoates.
The compound, 5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid, including the salt forms thereof, is known to have herbicidal activity. According to a particular herbicidal treatment, it has been proposed to apply this compound in a post-emergence fashion to control weeds, especially broadleaf weeds, in soybean fields. Accordingly, in such an application, a herbicide must possess the following two properties at the applied dosage rate: (1) the ability to control the target weeds; and (2) the ability to remain safe to the soybeans.
In attempting to improve on the herbicidal properties of 5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid and salts thereof, various derivatives of these compounds have been proposed including alkyl and cycloalkyl esters, alkylthio esters, phenyl ester, alkyl and dialkyl amido and benzoyl chloride forms. U.S. Patents which describe such compounds and the like include Nos. 3,652,645; 3,784,635; 3,873,302; 3,983,168; 3,907,866; 3,798,276; 3,928,416; and 4,063,929. For example, the simple methyl ester of the above-mentioned acid, i.e., methyl 5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoate, has been proposed, and it has been discovered that this compound has even greater herbicidal activity than 5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid with respect to various weeds, e.g. broadleaf weeds. However, it has also been discovered that methyl 5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoate has a relatively large degree of post-emergence herbicidal activity with respect to crops. Consequently, methyl 5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoate should not be applied in a post-emergence fashion to control broadleaf weeds in soybeans, because this compound tends to kill soybeans along with the weeds in such applications.
It has even been reported that the sodium salt of 5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoate tends to cause some initial damage to soybeans when applied in a postemergence fashion to control weed in soybean fields (see R. Y. Yih, "TODAY'S HERBICIDE: BLAZER TM-A New Postemergence Herbicide", Weeds Today, Vol. 12, No. 1, page 14, Early Spring 1981). Although the soybeans have been observed to recover from this initial damage, it would be desirable to develop compounds which give a lesser degree of initial soybean damage.
Accordingly, there is a need in the art for compounds which have a desirable combination of herbicidal properties with respect to weed activity and crop safety.